Laser Speckle Rheology (LSR) is an optical methodology for assessing the viscoelastic properties of materials with several industrial, biological, and medical applications. The quantification of the viscoelastic modulus, G*(ω), of a material in LSR may be effectuated, for example, by analyzing the temporal fluctuations of speckle patterns. While the size of scattering particles within the material also influences the rate of speckle fluctuations (independently from the contributions of the mechanical properties of the sample on such rate), the estimation of the viscoelastic properties made to date in related art was neglecting this factor, which in some cases could potentially lead to inaccurate estimates of G*(ω) and erroneous characterization of materials (for example, erroneous characterization of viscoelastic properties in biological fluids, such as blood and its components, the knowledge of which is rather critical in biological and medical applications, or in industrial polymers, substance or fluids, food or dairy products). There remains a need, therefore, to account for the influence of particle size on the characterization of materials with LSR.